1. Field of the Invention
The present invention relates an an apparatus such as a digital exchanger, for example, in which a plurality of slave units are controlled by a master unit, and more particularly to a method and apparatus for transferring data such as alarm, status and so on between the respective units.
2. Description of Related Art
FIG. 1 is a schematic diagram of a communication apparatus such as a digital exchanger, for example, to which the present invention is applied.
The communication apparatus shown in FIG. 1 is composed of one master unit MU and four slave units SU0, SU1, SU2 and SU3, and the respective slave units SU0, SU1, SU2 and SU3 are controlled by the master unit MU to exchange telephone lines.
In addition, to the master unit MU, a computer MUc is connected through a cable CB and also to the respective slave units SU0, SU1, SU2 and SU3, computers are connected respectively.
FIG. 2 is a block diagram of configuration for explaining a data transferring method which has been conventionally performed between the master unit MU and the respective slave units SU0, SU1 . . . and SUX in such a communication apparatus shown in the aforementioned FIG. 1.
The master unit MU and the respective slave units SU0, SU1 . . . SUX are connected by signal lines L1, L2 and L3 respectively. Clock CLK is given from the master unit MU to the respective slave units SU0, SU1 . . . and SUX through the signal line L1, and frame pulse FP is given through the signal line L2. And from the respective slave units SU0, SU1 . . . and SUX to the master unit MU, transfer data TD is sent through the signal line L3.
To the respective slave units SU0, SU1 . . . and SUX, data ID0, ID1 . . . and IDX each specifying each of the units are given, for example, by a digital switch and the like, and the respective units store data D0, D1 . . . and DX each data being status showing each state, alarm informing abnormal occurrence due to condition, and so on.
The master unit MU takes in data D0, D1 . . . and DX each data being alarm, status and so on, held by the slave units SU0, SU1 . . . and SUX and stores them in data memory MUa, and sends data in a data memory MUa to a computer MUc.
The computer MUc performs a necessary processing using or according to data having been taken in from the master unit MU.
FIG. 3 is a timing chart of a conventional method done by the configuration shown in FIG. 2, and it is a method disclosed as a prior art also, for example, in Japanese Patent Application Laid-Open No. 3-143047.
As aforementioned, the master unit MU gives clock CLK and frame pulse FP which makes predetermined cycles of the clock CLK as one cycle to the slave unit SU0, SU1 . . . and SUX respectively through the signal lines L1 and L2.
The respective units SU0, SU1 . . . and SUX send the data D0, D1 . . . and DX, each data being status, alarm and so on held by each slave unit to the signal line L3 at a preset timing in one cycle (one frame) of the frame pulse FP. To be concrete, making rising of the frame pulse FP as a base timing, a predetermined number of the following clock CLK (predetermined clock cycles) are allocated as a data output period of the respective slave units SU0, SU1 . . . and SUX. The respective slave units SU0, SU1 . . . and SUX. The respective slave units SU0, SU1, . . . and SUX send the respective data D0, D1 . . . and DX to the signal line L3 at the timing of the clock CLK allotted to them respectively.
According to the above-described method to the master unit MU, the transfer data TD obtained by time-division multiplexing the data D0, D1 . . . and DX sent from the respective slave units SU0, SU1 . . . and SUX is inputted one at a time at a cycle of one frame pulse FP.
Since the conventional data transferring method adopts such a method as aforementioned, data transferring from the master unit MU to the slave units SU0, SU1 . . . and SUX, or data transferring between the slave units SU0, SU1 . . . and SUX can't be performed, therefore there are problems that, status, alarm and so on of the master unit MU cannot be referred to at the slave units SU0, SU1 . . . and SUX side, and each of the slave units SU0, SU1 . . . and SUX cannot refer to status, alarm and so on of the other slave unit.
And at one cycle of the frame pulse FP, since data is sent from the respective slave units SU0, SU1 . . . and SUX to the master unit MU respectively one at a time in a fixed order, in the case, for example, where order of data transfer is changed by giving priority orders to the slave units SU0, SU1 . . . and SUX, or where data is required twice from one slave unit, while one time from the other slave unit because there is a difference in importance between the slave units SU0, SU1 . . . and SUX, the conventional construction can't deal with such cases.
In the aforementioned Japanese Patent Application Laid-Open No. 3-143047, there is disclosed a method for setting priority orders to the slave units and allowing the slave unit having the highest priority order among the slave units each having a request for transmitting, to transmit data to the master unit. But, since the judgment of priority order of the slave units is performed by the master unit and judgment of whether or not the slave unit is allowed to transmit is performed by software, response time is required respectively.